Hemiptera

Kansas State University

Hemolymph is the circulating fluid or "blood" of insects. It moves through the open circulatory system, directly bathing the organs and tissues. Insect hemolymph differs substantially from vertebrate blood, with the absence of erythrocytes and a high concentration of free amino acids being two of the common distinguishing features. The main component of hemolymph is water, which functions as a solvent for a variety of molecules. Water in hemolymph makes up 20 to 50% of the total water in insect bodies, with larval stages generally having a larger relative hemolymph volume than adults. Hemolymph serves as a water storage pool for use by tissues during desiccation and as a storage depot for other types of chemicals. It also contains circulating cells called hemocytes. Hemolymph can function as a hydraulic fluid, for example, in the expansion of a newly molted butterfly's wings. Hemolymph serves important roles in the immune system and in transport of hormones, nutrients, and metabolites.